In the operation of a heavy duty diesel truck, particularly when carrying a heavy load, it is imperative from safety and economical standpoints that an effective braking apparatus be provided which may be readily controlled by the driver. It has been found helpful in this regard, to utilize the engine as an air pump discharging against a blocked exhaust passage to slow down the engine and accordingly the speed of the vehicle and, thus, enable the wheel brakes to function more positively and at the same time prolong the life of the brake shoes or discs which engage the wheels of the vehicle.
Various exhaust braking apparatus have heretofore been provided; however, due to various design characteristics they have been beset with one or more of the following shortcomings: a) the apparatus is of costly and complex construction, b) it is difficult and/or awkward for the driver to operate properly, c) it is incapable of modulating the apparatus to compensate for various operating conditions of the engine, and d) it is highly susceptible to malfunction requiring and inordinate amount of servicing and maintenance. In addition, exhaust braking apparatus of the butterfly type cannot be made sufficiently free from leakage and/or seizure to make them reliable and capable of substantial braking forces.